Reciprocating pump piston and rod connection



June 22, 1965 A. L. LEMAN 3,190,191

RECIPROCATING PUMP PISTON AND ROD CONNECTION Filed Oct. 3, 1963 2 Sh ets-Sheet 1 I m I i II I I I m I l I I i Izweuiofl: flflioalwL.Lman/,

fifties ilune H1965 A. L. LEMAN 3,190,191

RECIPROCATING PUMP PISTON AN'D ROD CONNECTION FSiEIB'E bet. 36, I953 2 Sheets-Sheet 2 United. States Patent C) 3,190,191 RECERGCATING PUMP PISTON AND ROD (ZONNECTKON V 7 Arthur L. Leman, P.0. Box 24063, Houston, Tex. Filed Oct. 3, 1963, Sci-No; 313,575 13 Claims. (Cl. 92243) This invention relates to reciprocating pumps, andparticularly double acting pumps used for circulation of drilling fluid or slush in oil well drilling operations, wherein alternating opposite pressures of substantial value are eX- perienced. The invention is concerned more particularly with the improvement of drilling pumps of the type in which the piston and rod assembly is by a tapered threaded connection adapted for quick, easy removal and replacement of the piston without disturbing the operative installation of the pump rod in the pump cylinder.

The invention aims to provide for the demountable piston and rod assemblies such as here concerned an improved construction and arrangement whereby the pump piston and rod comection is stressed and stabilized to presaaaiai provision and prest-ressed engagementof the plain piston and rod tapers of theinvention'serves adequately to seal as well as to afford axial or stabilizing rigidity to the connection.

My invention will be fully understood from the following specification taken together with the accompanying drawings, in which: a

FIG. 1 is a partly sectioned side View of a preferred embodiment of my invention wherein the piston and rod connection is fully assembled or made up;

FIG. 2 shows the connection similarly as in FIG. 1 but with the piston and rodv in. an intermediate state of assembly; and i FIG. 3 shows the FIG. 1 piston and rod connection 7 with the parts in an initial stage of assembly.

.In thedrawings the piston rod of a double acting reciprocating slush pump is indicated at 5, and is shown further to have an outer terminal portion 6 formed into three sections. The larger or inner section of the terminal portion is formed as a threaded taper or tapered section 7, and is of a length for good purchase by, or more vent unwanted Working loose of the piston from the rod 7 in service. i

In the operation of oil well drilling pumps the presence of abrasive matter or slush in the pump fluid inevitably causes wear limiting the working life of and requiring the occasional replacement of the piston. This necessity for replacement of the pump piston resulted in the development of a pump piston and rod connection, as shown in the Leman Patent 2,741,618, wherein the construction and arrangement of the 'piston'and rod. connection was made such that the piston could be changed without removing the rod from the pump.v This quickly demountable form or type of pump assembly was accomplished, as shown in my mentioned prior patent, by means of a threaded tapered connection of the piston to the rod.

- However, operating experience showed that this joining or securing of the piston to the rod only through a tapered threaded length had the'disa-dvantage of worlding loose in service. That is, undue wear and slippage of the,

threaded surfaces was experiencedwith the mentioned prior construction, which was thereby. shown to lack sufficient axial rigidity to withstand the extreme slush pump service conditions, involving the rapid reciprocation particularly for secure threaded engagement with, a cor- ''responding or mating piston portion as hereinafiter expl-a-ined. Threads of varying taper and pitch may be employed on this threaded taper section 7, which may have fior example, a ,5 in. per foot on diameter taper and length 8, said intermediate straight section or length terdesired axial rigidity to Withstand theextreme pressure and abrasive wear conditions of reciprocatingslush pump service. The novel pump rod and piston connection hereof is further characterized in that the threaded and plain tapers of the piston are predeterminedly'smaller than the threaded and plain tapers of the rod, whereby when the assembly is made up it has greatlyincreased resistance to the forces tending to induce rocking of the parts and the wearing thereby of the threads thesebeing the forces which have heretofore caused a loosening of the assem bly and ultimately the backing off of the piston from the rod. v 7

Another feature of the invention is that, whereas in the prior Lemanpatent construction above referred to the bore of the piston core was required to be sealed, by an end cap which served to trap foreign matter passing the threads of the connection, the piston may more cheaply and easily be formed hereunder with a central axial pas-' sage cut all the way through the piston core, in'that the face as later mentioned;

minating outwardly in a right angular reduction or flat end face 9, and said flat end face 9 defining with said generally cylindrical lengths an intermediate external shoulder, or shoulder section, of said terminal rod portion. The terminal rod portion 6 is formed outwardly of said intermediate shoulder as a plain taper'ortapered section 10, which outer section 10 tapers down from end 'face 9 and is of appreciable longitudinal extent, whereby to fiorm a sufiicient or suitable pistons supporting or hearing sur- The plain tapered section 10 may be formed with varions tapers similarly as the threaded tapered section'7, including preferably a slightly larger or steeper taper than that of threaded tapered section 7, the plain tapered section herein having, by wayof example, a /2" per foot on diameter taper, as compared with the aforementioned H taper of the threaded tapered section.

Concentrically received on the terminal portion 6 of the pump rod 5 is apiston having a core 11 formed with a central transversely extending portion to which is intimately bonded av circumferential rubber packing comprising the oppositely projecting, radially flexing portions or lips 12,13, the said lips defining with the medial core portion a generally cylindrical surface for sliding contact with the cylindrical wall or liner of thepump during The core passage is formed with a threaded taper 15 at said inner hub 14,'the taper 15 extending in the illustrated embodiment to about the mid-point'of the core 11 for the desired substantial threaded engagement and bearing support of the piston, and more particularly the inner side thereof, on the rod.

Fatented June 22, 1965 transverse end face or wall 18 about midway or more of the length of hub16. This'intermediate core passage I portion 17 gradually tapers from the diameter of the roots of the threads 15 towards the diameter'of the cylindrical rod portion 8, and reduces to a minor cylindrical length 17a fitting closely around that mating rod surface 8. The

right angular inset of the core passage at end face 18 will be understood to define with intermediate passage portion 17a an internal shoulder faced oppositely to and proportioned to abut oroppose the mating external shoulder 8, 9 of rod 5. p i

In accordance with the invention,*the pistoncore 11 further has a cylindrical sleeve-19 integrally projected beyond hub 16 and also the packing 13, and which is formed at the core passage with a plain taper 20 generally conformant to the plain taper 10 of rod 5, whereby the sleeve 19 provides bearing support for the piston on the rod at the outer side of core 11.'- Sleeve 19-20 is seen also as formed with a number of longitudinal recesses 21 stressing of thefplain piston taper. 20 at a faster rate than the threaded piston taper 10. Thus in the present embodiment and with the tapers as above mentioned the advance of the threads through four turns will produce about .008 in. interference, and the relative closing of the plain tapers the longitudinal distance of one turn of the threads will produce about .005 in. interference on said plain tapers. It will be seen, then, that'the gaging or proportioning of the rod and piston under the invention is such as to produce,.by the closing to metal.-to-metal positive surface engagement of the parts, both a circumferential and a longitudinal stressing of the piston whereby the piston threads 15 are tensioned on the rod threads-7 both radially and axially of the assembly. In this way the piston and rod connection is afforded the needed'axial rigidity, stabilizing the piston on the rod and preventing relative movement of the parts such as heretofore producing wear and loosening of the threads.

It will be appreciated also that the conformant tightfitting engagement of the plain tapers 10, 20 'of the rod and piston adequately seals the connection againstescape of fluid or foreign matter past the threads'7, 15 'eliminating any need for an end cap or closure means such as would tend to weaken the piston core andrender'it more for rotative engagement by a tool or wrench such as con ventional and therefore not shown, wherebyjupon engagement and manipulation of the tool the piston may be quickly and easily backed off the rod while'that remains in normal use position in the pump cylinder.

Further in accordance with the invention, the threaded and plain tapers 15, 20 of the piston are deliberately made smaller than the mating tapers 7, of the rod, 7

whereby when the connection is fully made up the piston and more particularly its inner hub 14 and outer sleeve 19 are stresscd in circumferential tension. In addition, the relative extent and proportioning of the parts is so arranged undcrthe invention that as the piston is advanced over the end of'the rod the, threadedtapers 7, are rotated together a number ofgturns before the plain tapers 10, are initially engaged, and the plain tapers are in turn initially engaged at a point in the relative closing of the rod and piston before the shoulders 9, .18 are brought:

for gaging purposes, are not necessary to'the'invention construction. Thus the plain tapers 10, 20 mayalter natively be formed as an extension of substantially the same conical surface as the threaded tapers 7, 15, and the threaded and plan taper engagement may alternatively be delineated or diiferentiated merely by an intervening recess in or enlargement of the piston core passage herein'shown and described, the gaging is; such that the corresponding tapers 7, 15 of the rod and the pistonare threaded together about three: turns before the conformant I plain tapers 10, -20 of the rod and the piston are brought into positive metal-to-metal contact, and the making up of the assembly proceeds through about one more turn,

vance of the parts intocompressively stressed positive contact engagement. s e

In the making up :of the invention assembly or connection, then, the piston is'slid onto the rod and rotated by hand, with the threads of the inner tapers 7, 15in full circumferential engagement, through the necessary number of turns. This will first bring the plain tapers 10, 20 into engagement The available further rotation of the parts will be understood to subject both piston excostly to make.

It has been demonstrated by actual'use of the connec tion on a slush pump assembly employing'a pisto 'n of" 6 /2 in. size and subject to working pressures above 3000 lbs. per square inch, that the invention solves the stated problem in the manner herein described.

My invention is not limited to the particular embodi-i i ments thereof illustrated and described herein, andI se forth its scope in my following claims: V I claim: 7 1 1. A double acting reciprocating pump piston androd assembly comprising a piston rod having an outer ter-; minal portion; an inner threaded tapered section formed on said terminal portiomand outer plain tapered section formed'on said terminal portion; a piston comprisinga transversely extending metallic core; an axial passage formed through said core whereby it is receivable on said terminal portion of said rod; anjinner hub extension in i tegrally projected at oneside of said core and formed at. said passage with a threaded taper for conformant;fition said threaded tapered sectionnof said rod; and an outer hub extension integrally projectedrat'the other side of E said "core and balancing saidinner hub extension, sa id outer hub'ex'tension. formed at said core passage with a plain taper for conformant fit on said plain tapered .sec- 1 tion of said rod; and said threaded and plain tapers of 1 said piston hub extensions being predeterminedlytsmaller, than' said threaded and plain'tapered sections of saidter-i rriinal rod portion, whereby when said piston 'is advanced 2 over said rod to operative position said threadediand plain piston hub tapers are prestressed in circumferential tension, and said pump piston and rod assembly ;is af-- forded axial rigidity to prevent said threaded .pistonhub, i i taper from working loose from said threaded tapered rod section. p I v a 2. 'A double "acting reciprocating pump piston androd assembly according to claim 1 wherein the longitudinal spacing and relative proportions of the tapered rod sec-1 tions and piston hub tapersis such that the innerthreaded tremities to circumferential stress, as already explained V and also to stress the piston in longitudinal tension. This longitudinal tension will be seen to be produced by the tapered pair is threaded together three turnswhen the outer plain tapered pair makes contact. I

3. A double. acting reciprocating pump piston andj 7 assembly according to claiml wherein the threaded taper 1sabout W in. per foot'on-diameter, and the plain taper? isabout /2 in. per foot on diameter, whereby when the piston and rod are fully made up there is about 1,005 infl V interference in'the plaintaper and about .008 in. inter-- ference in the threaded taper. V 4. A double acting reciprocating pump I rod and piston assembly comprising a cylindrical pump rodhav'ing a" piston receiving portion, an inner threaded taper formed f on said portion, an outer plain taper formed on said rod portion, an annular piston comprising a transversely extending metallic core, a central bore formed axially through said core for reception of said piston on said rod, a threaded taper formed in a length of said bore extending to one sideof said core and for conformant fit on said threaded tapered rod section, a plain taper formed ina length of said bore extending. to the other side of said core, said plain taper of said bore adapted for conformant fit on said plain tapered section of said rod, said threaded and plain tapers of said rod'and piston being constructed and arranged such that when said assembly is made up the threaded tapers are'turned a number of ,times before the plain tapers are engaged, and such that the plain tapers are engaged before the assembly is assembly according to claim 4 wherein the threaded tapers are made up three turns when the plain tapers are brought into contact.

6. A double acting reciprocating pump piston and rod assembly according to claim 4 wherein the plain tapers make. contact about one turn of the threaded tapers before the assembly is fully made up.

7. A double acting reciprocating pump piston and rod assembly according to claim 4 wherein said core has at said plain taper alongitudinal extent presenting thereon a non-round formation for engagement by a tool for backing said piston off said rod.

8. In a double acting reciprocating pump piston and rod assembly as defined in claim 4, a shoulder formed on said pump rod portion adjacent said threaded taper, a shoulder formed on said piston bore adjacent its said threaded taper, said rod and pistonshoulders oppositely faced and abuttively engaged when said assembly is fully made up. a

9. A double acting reciprocating pump rod and piston assembly comprising a piston rod having an outer terminal portion, and on said portion an inner threaded taper and an outer plain taper; and a piston received on said rod and comprising a core having a central radially extending said passage formed at said inner hub with a threaded taper for threaded engagement on said threaded rod taper, and formed at said sleeve formation With a plain taper for conformant fit on said plain rod taper.

10. A double acting reciprocating pump piston and rod assembly according to claim 9, wherein said threaded and plain piston tapers are predeterminedly smaller than said threaded and plain rod tapers, whereby when the assembly is made up the threaded and plain piston tapers are stressed in circumferential and also longitudinal tension such that the assembly is aiforded greatly increased axial rigidity and resistance to loosening of the threaded engagement of the piston on the rod subject 'to' the pres- 1 sures on and reciprocating action of the pump. i v

11. A double acting reciprocating pump rod and piston assembly comprising a cylindrical piston having longitudinally opposite sections and a central bore extending continuously through both sections, said bore at one section being tapered and circumferentially threaded and at the other section being plain tapered, said assembly further comprising a piston rod having adjacent the free end a longitudinally tapered and circumferentially threaded portion with threading comformant to that of said first piston section, said rod also having in similar longitudinalspacing from said threaded portion a nonthreaded plain portion tapered in such relation to that of said other piston section as to form therewith a fluid seal upon making up of the assembly into operative status.

12. A double acting reciprocating pump rod and piston assembly according to claim 11'wherein one said section of the piston bore is of smaller diameter than the corresponding portion of the piston rod received therein.

13. A double acting reciprocating pump rod and piston assembly according to claim 11 wherein both said References Cited by the Examiner UNITED STATES PATENTS 1,849,067 3/32 Bridges 287- 2,499,662 3/50 Mattingly 92253 2,528,104 10/50 Young 287-20 RICHARD B, WILKINSON, Primary Examiner. KARL I. ALBRECHT, Examiner. 

1. A DOUBLE ACTING RECIPROCATING PUMP PISTON AND ROD ASSEMBLY COMPRISING A PISTON ROD HAVING AN OUTER TERMINAL PORTION; AN INNER THREADED TAPERED SECTION FORMED ON SAID TERMINAL PORTION; AND OUTER PLAIN TAPERED SECTION FORMED ON SAID TERMINAL PORTION; A PISTON COMPRISING A TRANSVERSELY EXTENDING METALLIC CORE; AN AXIAL PASSAGE FORMED THROUGH SAID CORE WHEREBY IT IS RECEIVABLE ON SAID TERMINAL PORTION OF SAID ROD; AN INNER HUB EXTENSION INTEGRALLY PROJECTED AT ONE SIDE OF SAID CORE AND FORMED AT SAID PASSAGE WITH A THREADED TAPER FOR CONFORMANT FIT ON SAID THREADED TAPERED SECTION OF SAID ROD; AND AN OUTER HUB EXTENSION INTEGRALLY PROJECTED AT THE OTHER SIDE OF SAID CORE AND BALANCING SAID INNER HUB EXTENSION, SAID OUTER HUB EXTENSION FORMED AT SAID CORE PASSAGE WITH A PLAIN TAPER FOR CONFORMANT FIT ON AID PLAIN TAPERED SECTION OF SAID ROD; AND SAID THREADED AND PLAIN TAPERS OF SAID PISTON HUB EXTENSIONS BEING PREDETERMINEDLY SMALLER THEN SAID THREADED AND PLAIN TAPERED SECTIONS OF SAID TERMINAL ROD PORTION, WHEREBY WHEN SAID PISTON IS ADVANCED OVER SAID ROD TO OPERATIVE POSITION SAID THREADED AND PLAIN PISTON HUB TAPERS ARE PRESTRESSED IN CIRCUMFERENTIAL TENSION, AND SAID PUMP PISTON AND ROD ASSEMBLY IS AFFORDED AXIAL RIGIDITY TO PREVENT SAID THREADED PISTON HUB TAPER FORM WORKING LOOSE FROM SAID THRADED TAPERED ROD SECTION. 